This invention relates to lubricating coatings for use on metallic workpieces during forming processes and, more particularly, to a method for stabilizing and prolonging the effectiveness of a coating-forming bath containing sodium and/or potassium silicate.
A coating bath of the type to which the present invention is directed, that is, one containing sodium and/or potassium silicate is described in detail and claimed in the copending application of the present applicant, Ser. No. 631,732, filed Nov. 13, 1975, assigned to the assignee of the present application, and now U.S. Pat. No. 4,088,585, granted on May 9, 1978. The entire disclosure of said application Ser. No. 631,732 is expressly incorporated here by reference and, therefore, will not be repeated here. However, it may be noted here that coating formulations provided in accordance with said copending application on a commercial production scale have been used with outstanding success. For example, a production scale coating bath containing upwards of 1,000 gallons (3,785 liters) was used over a period of eight months to coat more than 530,000 lb (240,000 kg) of wire, which in the form of coils, was dipped into the bath. During that eight-month period, water and the aliquot portions of the bath ingredients calculated from the amount of coating material removed from the bath in the coating process, were from time-to-time added to maintain the desired minimum depth and content of the coating bath. After completion of eight months of successful coating operations, the coatings formed on coils thereafter dipped in the bath showed less than optimum properties, particularly in that the adherence of the coating to the wire substrate left much to be desired.
Such deterioration in the coating bath, though occurring relatively slowly and after prolonged use, nevertheless involves substantial expense as may be most readily appreciated when the cost of the molybdenum disulfide involved is taken into account. On the other hand, when the wire to be coated is drawn as one or more strands through a relatively small container, the problems associated with the long-term exposure of a relatively large coating bath to the ambient atmosphere or conditions encountered in the usual commercial production of coated wire treated in the form of coils, would not be expected to be encountered. Nevertheless, when, as may often be most convenient, the coating is applied using a coil-dipping technique, the inconvenience and expense of discarding a substantial amount of bath formulation and providing a bath made from new ingredients is a disadvantage.